1. Field of the Invention
The invention pertains to apparatus and a method for volume reduction of aqueous hazardous waste through solar evaporation particularly in areas having marginal or even negative annular net evaporation rates.
2. Description of the Prior Art
The greatest part of hazardous waste which must be disposed of in some fashion occurs in liquid or semi-liquid form. Traditionally, aqueous hazardous waste material has been treated and disposed of through one or a combination of: recycling or reclamation, incineration, water discharge of the aqueous portion after the pollutants have been removed or detoxified, and disposal on land where the untreated liquid is soaked or injected into the void spaces of soil and any solids are securely land-filled.
These treatment and disposal methods are extremely cost ineffective when dealing with high volumes of aqueous waste containing low concentrations of mixed pollutants, such as salts, heavy metals, and low vapor pressure organic materials. Recycling or reclamation works acceptably well only on high volumes of concentrated materials of uniform chemical constituency and, thus, high volumes of liquid with low concentrations of mixed pollutants can generally not be recovered by such methods. Incineration is not cost effective as large amounts of supplemental energy must be added to evaporate the water portion of the pollutants in order to oxidize the low vapor pressure organic materials and metals. The remaining metals and salts create potential air pollution and equipment damage problems. Removal or detoxification of pollutants prior to water discharge of the aqueous portion requires large initial capital expenditures and high operating cost for removal of the mixed pollutants. Additionally, the presence of salts and heavy metals excludes biological treatment of the organic portion as these pollutants in any significant concentration are biocides. Disposal of untreated liquid into soil by injection or soaking is generally cost ineffective as the difference between the natural soil moisture content and the maximum saturated moisture content without leachate generation is usually small and uniform mixing of the soil with the liquid is mechanically difficult to accomplish. Use of better absorbing mediums such as solid waste in place of soil may be cost effective, but such techniques may only be used in areas of high solid waste production. The potential of leachate generation if the material is over-saturated is nonetheless still present.
One solution to the treatment and disposal of high volumes of aqueous waste with low concentration of mixed pollutants such as salts, heavy metals, and low vapor pressure organics has been to evaporate off the water portion of the waste, leaving the pollutants in a concentrated form, thus making the four treatment methods mentioned above much more cost effective. However, use of fossil fuels to generate heat for evaporating the water phase is very cost ineffective as the cost of the fuel is more than the resulting treatment savings. For example, it would take 6,787,000 gallons of 18,500 BTU/lb. fuel oil to evaporate 100,000,000 gallons of 62.degree. F. water at standard conditions assuming a 100% heat transfer efficiency, which is thermodynamically impossible.
Solar evaporation has been found to be a cost effective alternate volumetric reduction method in areas of high net evaporation rates and low land cost and impermeable soils. Desert areas are particularly well suited for such techniques. Many areas may have the low cost, impermeable land necessary for solar concentration of aqueous hazardous waste pollutants but, unfortunately, have a low or negative net annual evaporation rate caused by high rainfall and high humidity which has heretobefore prevented solar evaporation techniques from being successfully applied.